Chapter 20Electrochemistry

West Valley High School

General Chemistry

Mr. Mata

Standard 3h

Students will know how electrochemical cells work, and how to identify the cathode and anode.

Essential Question

How does an electrochemical cell operate and what is the relationship to redox reactions?

Objectives

Distinguish between oxidation and reduction.

Identify the path taken by electrons in an electrochemical cell.

Describe how current flows in a voltaic cell.

Oxidation and Reduction“LEO” goes GER

Any chemical process in which elements undergo changes in oxidation number is an oxidation-reduction reaction.

This name is often shortened to redox reaction.

Reactions are carried out in electrochemical cells.

Oxidation

Reactions in which the atoms or ions of an element experience an increase in oxidation state.

“Leo” – Lose electrons: Oxidation

A species whose oxidation number increases is oxidized.

Oxidation of Zn

Zn (s) Zn2+ (aq) + 2e-

Zn lost electrons (0 +2).

Zn is being oxidized (LEO).

Oxidation takes place at the anode.

Reduction Reactions in which the oxidation state of

an element decreases.

“GER”: Gain electrons - reduction

A species that undergoes a decrease in oxidation state is reduced.

Reduction of Cu Cu2+ (aq) +2e- Cu (s)

Cu2+ gains electrons (+2 0).

Cu2+ is reduced (GER).

Reduction takes place at the cathode.

Together, 2 half reactions can be written together to show a redox reaction.

The number of electrons lost must equal the number electrons gained.

Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)

How are electrochemical processes carried out?

• Both oxidation and reduction must occur in an electrochemical reaction.

• The two half-cells taken together make an electrochemical cell.

How are electrochemical processes carried out? Half-cell: A single electrode (anode or

cathode) immersed in a solution of its ions.

An electrochemical cell will contain 2 half-cells (1 containing the anode, other cathode).

Electrons can be transferred from one half-cell to the other through an external connecting wire called a circuit.

• Electricity is the movement of electrons along a given path.

• The circuit is a closed loop path, so the movement of electrons through the wire is balanced by the movement of ions in solution.

• Electrode is a conductor used to establish electrical contact with a nonmetallic part of a circuit, such as an electrolyte.

Electrochemical Cells

19.2

spontaneousredox reaction

anodeoxidation

cathodereduction

• Voltaic cells use spontaneous oxidation-reduction reactions to convert chemical energy into electrical energy.

• Voltaic cells are also called galvanic cells.

• The most common application of voltaic cells is in batteries.

Batteries

19.6

Leclanché cell

Dry cell

Zn (s) Zn2+ (aq) + 2e-Anode:

Cathode: 2NH4 (aq) + 2MnO2 (s) + 2e- Mn2O3 (s) + 2NH3 (aq) + H2O (l)+

Zn (s) + 2NH4 (aq) + 2MnO2 (s) Zn2+ (aq) + 2NH3 (aq) + H2O (l) + Mn2O3 (s)

Chapter 20 SUTW Prompt Describe the role of the anode and

cathode in an electrochemical cell. Complete a 8 -10 sentence paragraph

using the SUTW paragraph format. Hilight using green, yellow, and pink.

Due Date: Tomorrow (start of class).